Description: (Applicant's Description) At UCSD many investigators are now conducting research which requires the microscopical analysis of human and murine tumors and their cognate normal tissues. Others are examining the details of changes induced in embryonic and adult animals by genetic and epigenetic intervention, so as to understand the mechanisms regulating normal and neoplastic development. All of these research workers studying topics relevant to the cancer problem need ready, affordable access to high quality histological and immunohistochemical technical services and to expert histopathological and embryological advice. This resource already provides pivotally important services to the Members of the Center and its importance will grow as it becomes more widely appreciated that microscopical, tissue-based evaluation of neoplastic lesions and their precursors is the cornerstone of good reliable research technique in cancer research. It provides confirmation of the neopla stic nature of a given sample and accurate pathological grading and staging. For the correlation of laboratory data with the diagnostic category of a lesion, it is indispensable and it also provides vital quality control of the presence of tumor tissue in a sample before biochemical or molecular biological analysis begins. Furthermore, it is essential for establishing the absence of tumor in tissue that is regarded as a normal control for such experiments. Without such essential information, much time, effort and money can be wasted and conclusions can be meaningless. The goal of the Histology and Immunohistochemistry Shared Resource is to provide these facilities to peer-reviewed Cancer Center Members and affiliated investigators. The Resource (formerly known as the Tissue Bank) has grown, during the last four years, into a widely used recharge facility and has been strengthened with additional staff. Its mission for the next funding cycle is to liaise closely with other UCSD NCI-funded Shared Resources, especially Animal Experimentation, Informatics, Molecular Pathology and Transgenic Mouse to create a superbly interactive group for the analysis of samples of human tissue, experimental animals carrying tumors, experimental animals carrying transgenes and "knock-out" mice.